JPH11204242A - Induction heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the breakage of a switching element in an abnormal conduction by connecting D.C. power supply, a heating coil and the switching element in series and installing a self-short-circuiting means that short-circuits itself when the voltage across the switching element is not less than a predetermined value. SOLUTION: A switching element 13 connected parallel with a reversely conductive diode 14, a heating coil 15, and a D.C. power supply 11 are connected in series. A self-short-circuiting means 18 makes the switching element 13 short- circuit itself when the voltage across the switching element 13 becomes not less than a predetermined value (a value higher than a voltage generated in a normal operation and lower than the withstand voltage of the switching element 13). Thus, when a voltage exceeding the withstand voltage of the switching element 13 is generated in it due to a power supply abnormality, oscillation abnormality or the like, the switching element 13 itself short-circuits itself so that its breakage can be prevented. This dispenses with a protective circuit, simplifies the structure, and prevents the breakage of the switching element 13 even in the case of high surge voltage or the like generated by external noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating device such as an induction heating cooker used in ordinary households and restaurants, and more particularly to an inverter circuit configuration and a control method thereof.

[0002]

2. Description of the Related Art A conventional inverter circuit configuration and control method of an induction heating apparatus will be described with reference to FIGS.

FIG. 16 shows a basic circuit of an inverter of an induction heating device. Reference numeral 1 denotes a DC power supply, which is obtained from a commercial AC power supply via a rectifier. Reference numeral 2 denotes a heating coil, on which an object to be heated is placed and heated by a high frequency magnetic field from the heating coil 2. Reference numeral 3 denotes a resonance capacitor connected in parallel with the heating coil 2, and 4 denotes a switching element, and a high-frequency current is supplied to the heating coil by turning on / off the element. The switching element 4 uses an IGBT that requires much less driving power than a bipolar transistor or the like, and has a withstand voltage of 900 V and a current rating of 60 A. Reference numeral 5 denotes a reverse conducting diode connected in parallel to the switching element 4, and reference numeral 6 denotes a control circuit that detects a collector-emitter voltage of the switching element 4 and controls on / off of the switching element 4.

FIG. 17 is a diagram showing waveforms at various points during the operation of the inverter of FIG. (A) is a drive signal of the switching element 4 outputted from the control circuit 6, and when HIGH, the switching element 4 is turned on. (A) shows the current flowing through the switching element 4 and the reverse conducting diode 5. (C) is a voltage generated between the collector and the emitter of the switching element 4.

FIG. 18 is a diagram showing a protection operation for the switching element 4 of the control circuit 6 in the event of an abnormality such as a power supply fluctuation or a malfunction of the oscillation circuit due to external noise. In other words, when returning from an instantaneous power failure or during a lightning surge,
When the switching element 4 is turned off in a state where the current peak is large, the switching element 4 has a value higher than the resonance voltage generated during the normal operation, and may exceed the breakdown voltage of the switching element 4 and may be destroyed. A predetermined value that is higher than the generated voltage and lower than the withstand voltage of the element is provided, and the control circuit 6 detects the voltage across the switching element 4. Is to stop the drive signal. In this case, the voltage to be detected is set as the collector voltage of the switching element 4, but it is also possible to detect the input voltage of the inverter.

[0006]

However, the above-described conventional induction heating apparatus has the following problems. First
The problem with the above is that the protection operation at the time of the abnormality is performed in such a manner that the element stops oscillating after the occurrence of the abnormality. The element 4 is destroyed.

A second problem is that the protection circuit in the control circuit 6 has a close relationship with an inverter constant (electric constants of the heating coil 2 and the resonance capacitor 3 and the like). Because the waveform of the voltage between the collector and the emitter is different), it is necessary to review circuit constants every time various induction heating devices are developed, which is one of the bottlenecks in the development man-hour.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned conventional problems and to realize a safe induction heating device having a simple structure capable of preventing the switching element from being destroyed even though the protection circuit is unnecessary. .

[0009]

In order to solve the above problems, the present invention provides a DC power supply, a heating coil, a resonance capacitor connected in parallel to the heating coil, a switching element, and a switching element. A reverse conducting diode connected in parallel, and a control circuit including an oscillation circuit that generates an on / off signal for the switching element, wherein the DC power supply, the heating coil, and the switching element are connected in series, and the switching element is And an induction heating device having self-shortening means for self-shortening when the voltage across the terminals is equal to or higher than a predetermined value.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 comprises a DC power supply, a heating coil, a resonance capacitor connected in parallel to the heating coil, a switching element, and a reverse conducting diode connected in parallel to the switching element. A control circuit including an oscillation circuit that generates an on / off signal for the switching element, wherein the DC power supply, the heating coil, and the switching element are connected in series, and the switching element has a predetermined voltage at both ends. An induction heating device having a self-shortening means for self-shortening when the value is equal to or more than the value.

According to this configuration, by setting the predetermined value to be lower than the withstand voltage of the switching element, the switching element itself can be short-circuited (self) even if a voltage higher than the withstand voltage of the element is generated due to some abnormality. Since it is clamped to avoid destruction, the protection by an external circuit (a protection operation of detecting an abnormality by the external circuit and turning off the switching element) which is conventionally required is not required.

According to a second aspect of the present invention, in particular, the switching element is a voltage-driven element such as an IGBT, and a Zener diode connected in series between the collector and the gate of the switching element is inserted. If the diode clamping voltage is designed to be lower than the breakdown voltage of the IGBT, the self-short circuit operation can be achieved with extremely few components.

According to a third aspect of the present invention, in particular, the switching element is a voltage-driven element such as an IGBT, and its gate is supplied with a voltage obtained by dividing the voltage across the switching element by resistance. By designing the resistance division value to be equal to or lower than the threshold voltage and equal to or higher than the withstand voltage of the switching element and equal to or higher than the threshold voltage, the self-short-circuit operation can be realized with extremely few components and at a lower cost than the configuration according to claim 2. can do.

According to a fourth aspect of the present invention, in particular, by self-shortening via a drive circuit of the switching element,
Since the gate voltage can be made sufficiently low during normal operation (at the time of off-state) as compared with the configuration of the third aspect, the design relating to the threshold voltage difference of the switching element can be designed. An induction heating device that does not need to be applied can be realized.

According to the fifth aspect of the invention, in particular, since the off state is continued for a predetermined time after the recovery from the self-short circuit, it is possible to prevent the switching element from being thermally damaged due to the continuous self-short circuit.

[0016] The invention according to claim 6 is characterized in that after the self-short-circuit recovery, the off state is continued for a predetermined time regardless of the on / off signal of the oscillation circuit. Even in an abnormal case, it is possible to prevent the switching element from being destroyed.

According to the present invention, in particular, the off state is continued for a predetermined time after the recovery from the self-short-circuit, and the oscillation state is set after the predetermined time. When the operation of the self-short circuit continues for a predetermined number of times when the voltage is generated, the OFF state is maintained for the predetermined time or more, for example, when the object to be heated by induction heating is in an abnormal state. For example, unnecessary oscillation can be reduced, and as a result, the loss of the switching element can be reduced.

According to the present invention, in particular, the off state is continued for a predetermined time after the recovery from the self-short circuit, and the oscillation state is established after the predetermined time. Is generated, and when the operation of self-short circuit continues for a predetermined number of times, the power supply is turned off for the predetermined time or more, and the abnormality is notified, so that the user can be notified of the abnormality. .

[0019]

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described. In FIG. 1, reference numeral 11 denotes a DC power supply, specifically, a commercial AC power supply is obtained via a rectifier. 13
Is a switching element, which is connected in parallel with the reverse conducting diode 14. Reference numeral 15 denotes a heating coil, though not particularly shown in the figure, on which an object to be heated such as a pot is placed. A resonance capacitor 16 is connected in series with the heating coil 15, and a resonance circuit is formed by these two components. Reference numeral 17 denotes a control circuit including an oscillation circuit 19, which controls the switching element 13. Numeral 18 denotes a self-shortening means. The voltage at both ends of the switching element 13 is higher than a predetermined value (specifically, higher than a voltage generated during normal operation.
The switching element 13 self-short-circuits when the voltage becomes equal to or higher than the withstand voltage of the switching element 13).

FIG. 2 shows the drive signal of the switching element 13 and the current (Ic) voltage (Vce) when the on / off timing of the switching element 13 is deviated due to some abnormality and a resonance voltage higher than that in the normal operation of the switching element 13 is generated. ) Waveform. As shown in the figure, when the switching element 13 is turned off in a state where the peak current is larger than the normal state, a high resonance voltage is generated in the voltage between both ends of the switching element 13. In addition, the switching element 13 is not short-circuited by itself and does not exceed the withstand voltage of the switching element 13.

FIG. 3 shows the switching element 1 during a self-short circuit.
When the voltage across the switching element 13 exceeds a predetermined value due to the self-shortening means 18 in the enlarged waveform of the drive signal 3, the current (Ic) voltage (Vce) and the drive terminal voltage (Vge),
The drive terminal voltage rises and exceeds the threshold voltage of the switching element 13 to cause a self-short circuit.

As is clear from the above description, according to the present embodiment, it is possible to obtain an induction heating apparatus with a simple structure and without breakdown voltage breakdown of the switching element 13 at the time of abnormality.

(Embodiment 2) Hereinafter, a second embodiment of the present invention will be described. FIG. 4 is a view showing a second embodiment of the present invention. In FIG. 4, reference numeral 21 denotes a self-shortening means 18 according to the first embodiment, in which a Zener diode and a diode connected in series are inserted between the collector and the gate of the switching element 13. Switching element 1
Reference numeral 3 uses an IGBT as a voltage control type element.
Other parts are the same as in the first embodiment. The clamp voltage of the Zener diode has the same predetermined value as in the first embodiment. The operation of this embodiment is the same as the operation of the first embodiment. As described above, the self-shortening means 18 can be realized with an extremely simple component configuration.

(Embodiment 3) Hereinafter, a third embodiment of the present invention will be described. FIG. 5 is a diagram showing a third embodiment of the present invention. In FIG. 5, reference numeral 22 denotes a configuration in which the voltage between both ends of the switching element 13 is resistance-divided, and the divided voltage is supplied to the gate of the switching element 13 by using the self-shortening means 18 of the first embodiment. Has been realized. The switching element 13 is a voltage-controlled element,
IGBT is used. Other parts are the same as in the first embodiment. As in the first embodiment, the voltage divided by the resistor is designed to have a value that does not exceed the threshold voltage of the switching element 13 and does not exceed the withstand voltage of the switching element 13 and exceeds the threshold voltage during normal operation. .

FIG. 6 shows the switching element 13 during a self-short circuit.
5 is an enlarged waveform of the drive signal, the current (Ic) voltage (Vce), and the drive terminal voltage (Vge). The operation of this embodiment is almost the same as that of the first embodiment, but the driving terminal voltage waveform (Vge) at the time of self-short circuit is slightly different due to resistance division. As described above, the self-shortening means 18 can be realized with an extremely simple component configuration, and can be realized with only the resistance as compared with the second embodiment, so that the cost is low.

(Embodiment 4) Hereinafter, a fourth embodiment of the present invention will be described. FIG. 7 is a diagram showing a fourth embodiment of the present invention. In FIG. 7, reference numeral 23 denotes the switching element 13.
24 is a switching element 13
Is a driving circuit. The both-ends voltage detection circuit 23 is configured to self-short-circuit the switching element 13 via the drive circuit 24 when a voltage equal to or higher than a predetermined value is generated. The switching element 13 is an IGBT as a voltage control type element.
Is used. Other parts are the same as in the first embodiment.

FIG. 9 shows the switching element 1 during a self-short circuit.
3 is an enlarged waveform of a drive signal, a current (Ic) voltage (Vce), and a drive terminal voltage (Vge). The drive circuit 24 does not have a steep drive terminal voltage waveform, but has a gentle waveform as shown in FIG. 8, because the limiting resistance for limiting the turn-on and turn-off of the switching element 13 is sufficiently large. The operation is almost the same as the operation of the first embodiment. As described above, the configuration is inexpensive as compared with the second embodiment (the voltage detection circuit at both ends is possible with simple components such as a resistor and a transistor), and the switching element is compared with the third embodiment. Therefore, it is not necessary to design the thirteenth threshold voltage.

(Embodiment 5) Hereinafter, a fifth embodiment of the present invention will be described. FIG. 9 shows a fifth embodiment of the present invention. In FIG. 9, reference numeral 26 denotes the switching element 13.
Is an oscillation circuit having a drive terminal voltage detection circuit for the switching element 13 and a time measuring means. Other parts are the same as in the first embodiment.

FIG. 10 shows a drive signal of the switching element 13 and a current (Ic) voltage (Vce) waveform when a high resonance voltage is generated in the switching element 13 due to some abnormality. Switching element 13 when surge voltage occurs
Is higher than the threshold voltage despite the fact that the oscillation circuit is outputting an OFF signal, the oscillation circuit 27 detects the voltage and sends the next transmission signal for a predetermined time set in the timer. Stop the signal. The reason why the predetermined time is provided is that the switching element 13 causes an instantaneous loss due to the self-short circuit, and the junction temperature increases transiently. 13 is to be protected.
Therefore, the design of the predetermined time is a guideline from the rise of the junction temperature due to the self-shortening of the switching element 13 to the return to the steady state.
About 0 ms is sufficient. By the above operation, even in a mode in which a high resonance voltage may be continuously generated such as in the case of a power supply abnormality, the self-short-circuit of the switching element 13 is one.
It is possible to prevent the destruction of the switching element 13 by turning.

(Embodiment 6) Hereinafter, a sixth embodiment of the present invention will be described. FIG. 11 shows a sixth embodiment of the present invention. In FIG. 11, 28 is an oscillation circuit, 29 is a drive circuit for driving the switching element 13, 30 is a protection circuit that detects the drive terminal voltage of the switching element 13 and lowers the drive terminal voltage to LOW for a predetermined time, and has a timer. ing. Other parts are the same as in the first embodiment.

FIG. 12 shows a drive signal of the switching element 13 and a current (Ic) voltage (Vce) driving terminal voltage (Vge) waveform when a high resonance voltage is generated in the switching element 13 due to some abnormality. When a high resonance voltage is generated, the drive terminal voltage of the switching element 13 is equal to or higher than the threshold voltage despite the fact that the oscillation circuit outputs an OFF signal. Therefore, the protection circuit 30 detects the voltage,
The drive terminal voltage of the switching element 13 is reduced to LOW for a predetermined time set in the timer means regardless of the presence or absence of a drive signal from the oscillation circuit side. The reason for setting the predetermined time is
This is to protect the switching element 13 in a case where a mode in which the self-shortening occurs continuously occurs because the switching element 13 instantaneously increases in loss due to the self-short circuit and the junction temperature transiently increases. . Therefore, the design of the predetermined time is a standard time from when the switching element 13 rises in junction temperature due to a self-short circuit to when the switching element 13 returns to a steady state.
ms is sufficient. With the above operation, in addition to the mode in which a high resonance voltage may be continuously generated, such as in the case of a power supply abnormality, the switching element 13 may not operate even when the operation of the oscillation circuit temporarily becomes improper for some reason. Only one short-circuit can prevent the switching element 13 from being destroyed.

Embodiment 7 Hereinafter, a seventh embodiment of the present invention will be described. FIG. 13 shows the seventh embodiment of the present invention. In FIG. 13, reference numeral 31 denotes a protection circuit, the operation of which is the same as that described in the sixth embodiment. 32 is a drive circuit for driving the switching element 13, 33 is an oscillation circuit for detecting the protection operation of the protection circuit 31, and 34 is a counting means for counting the number of protection operations of the protection circuit 31. Other parts are the same as in the first embodiment. FIG.
Is a drive signal of the switching element 13 and a current (Ic) voltage (Vce) waveform in a case where the object to be heated is abnormal.

In the case of the waveform shown in FIG. 14, a high resonance voltage is continuously generated, so that an abnormality in the load can be detected on the circuit side. In particular,
The protection operation of the protection circuit 31 is counted by the counting means 34, and when the count reaches a predetermined number or more, the oscillation circuit 33 stops the oscillation for a sufficiently long time. As described above, the unnecessary oscillation can be easily reduced on the circuit side when the heating operation is unnecessary such as when the load is abnormal.

Embodiment 8 Hereinafter, an eighth embodiment of the present invention will be described. FIG. 15 shows the eighth embodiment of the present invention. In FIG. 15, reference numeral 35 denotes a notifying unit for notifying an abnormality to the outside. In this embodiment, the LED is turned on to notify the user of the abnormality. The other parts are the same as in the seventh embodiment. As described in the seventh embodiment, when the protection circuit 31 enters a mode in which the protection operation continues for a predetermined number of times or more, the oscillation circuit 33 stops oscillating for a sufficiently long time.
Notifies the outside of the abnormality. As described above, the user can immediately know the abnormal state.

[0035]

As described above, according to the first aspect of the present invention, when a voltage exceeding the withstand voltage is generated in the switching element due to power supply abnormality, oscillation abnormality, etc., the switching element itself is self-short-circuited. As a result, a protection circuit with a large number of development steps for detecting voltage and stopping oscillation as in the related art is unnecessary.

In the present invention, the switching element can be prevented from being destroyed even at a high surge voltage or the like generated by external noise or the like, so that an extremely reliable induction heating device can be obtained.

Further, according to the second aspect of the present invention, the self-short-circuit operation according to the first aspect can be simply and reliably performed by the two components of the zener diode and the diode.

Further, according to the third aspect of the present invention, the self-shortening operation according to the first aspect can be performed only by the resistor, which is less expensive than the configuration according to the second aspect.

According to the fourth aspect of the present invention, the self-shortening operation of the first aspect is performed via the drive circuit of the switching element, so that the self-shortening operation is inexpensive as compared with the second aspect. This can be realized with a simpler design than the configuration described in claim 3.

According to the fifth aspect of the present invention, the oscillation is stopped for a predetermined time after the switching element self-short-circuits. Therefore, even if a continuous surge voltage is generated due to a power supply abnormality such as a lightning surge, the switching element is not used. It does not cause thermal destruction.

According to the sixth aspect of the present invention, the switching element is stopped for a predetermined time after the self-short circuit regardless of the presence or absence of a drive signal from the oscillation circuit. Even in the case of an abnormal drive signal, it is possible to prevent the switching element from being destroyed.

According to the seventh aspect of the present invention, it is possible to detect an abnormal load condition such as a no-load condition on the circuit side and prevent unnecessary oscillation from continuing.

According to the invention described in claim 8, in addition to the effect of the invention described in claim 7, it is possible to immediately notify an abnormal state to a user or the like.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an induction heating device according to a first embodiment of the present invention.

FIG. 2 is an operation waveform diagram in the case of an abnormality.

FIG. 3 is a diagram showing a protection operation at the time of abnormality.

FIG. 4 is a circuit configuration diagram of an induction heating device according to a second embodiment of the present invention.

FIG. 5 is a circuit configuration diagram of an induction heating apparatus according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a protection operation at the time of abnormality.

FIG. 7 is a circuit configuration diagram of an induction heating apparatus according to a fourth embodiment of the present invention.

FIG. 8 is a diagram showing a protection operation at the time of abnormality.

FIG. 9 is a circuit configuration diagram of an induction heating device according to a fifth embodiment of the present invention.

FIG. 10 is a diagram showing a protection operation at the time of abnormality.

FIG. 11 is a circuit configuration diagram of an induction heating device according to a sixth embodiment of the present invention.

FIG. 12 is a diagram showing a protection operation at the time of abnormality.

FIG. 13 is a circuit configuration diagram of an induction heating apparatus according to a seventh embodiment of the present invention.

FIG. 14 is an operation waveform diagram at the time of an abnormality.

FIG. 15 is a circuit diagram of an induction heating apparatus according to an eighth embodiment of the present invention.

FIG. 16 is a circuit configuration diagram of a conventional induction heating device.

FIG. 17 is an operation waveform diagram of the same.

FIG. 18 is an operation waveform diagram of the same.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 DC power supply 13 Switching element 14 Reverse conduction diode 15 Heating coil 16 Resonant capacitor 17 Control circuit 18 Self-short circuit 19 Oscillation circuit 21 Zener diode and diode 22 Resistance 23 Both ends voltage detection circuit 24 Drive circuit

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hidekazu Yamashita 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (8)

[Claims] 1. A DC power supply, a heating coil, a resonance capacitor connected in parallel to the heating coil, a switching element, a reverse conducting diode connected in parallel to the switching element, and an on / off signal of the switching element. And a control circuit including an oscillation circuit for generating the DC power supply, the DC power supply, the heating coil, and the switching element are connected in series. Induction heating device having 2. The induction device according to claim 1, wherein the switching element is a voltage-driven element, and the self-short-circuit means is configured to insert a zener diode and a diode connected in series between the collector and the gate of the switching element. Heating equipment. 3. The induction heating apparatus according to claim 1, wherein the switching element is a voltage-driven element, and the self-short circuit applies a voltage obtained by dividing a voltage between both ends of the switching element by resistance to a gate. 4. The switching device according to claim 1, further comprising a driving circuit for the switching element, wherein the self-short circuit means causes the switching element to self-short-circuit via the driving circuit when a voltage across the switching element is equal to or higher than a predetermined value. Induction heating equipment. 5. The switching element, after recovery from self-short circuit,
The induction heating device according to claim 1, wherein the off-state is continued for a predetermined time. 6. The switching element, after recovery from self-short circuit,
6. The induction heating apparatus according to claim 5, wherein the OFF state is maintained for a predetermined time regardless of the ON / OFF signal of the oscillation circuit. 7. An operation in which the switching element continues the off state for a predetermined time after self-short-circuit recovery and repeats oscillation again,
6. The induction heating device according to claim 5, wherein when the operation is performed a predetermined number of times or more, a long-time off state exceeding a predetermined time in the off state during the repetition is provided. 8. The induction heating apparatus according to claim 7, wherein when the operation of continuing the off state for a predetermined time after the self-short-circuit recovery and repeating the oscillation again is performed a predetermined number of times or more, the notification is made to the outside.